Dashpot



United States Patent DASHPOT Robert B. Gray, Erie, Pa., assignor to Erie Resistor Corporation, Erie, Pa, a corporation of Pennsylvania Application April 17, 1957, Serial No. 653,428

2 Claims. (Cl. 267-1) This invention is a liquid dashpot which is easily assembled and which is stable in operation over a wide range of temperatures. In a preferred form, the dashpot, piston and cylinder are molded plastic and the liquid is a silicone oil.

In the drawing, the single figure is a longitudinal section of the dashpot.

The cylinder of the dashpot comprises a tubular section 1 at opposite ends of which are fixed end caps or cylinder heads 2. These parts are made of one of the dimensionally stable thermoplastic elastomers such as nylon and are secured together by heat sealing the abutting surfaces. Prior to heat sealing, a piston 3, a spring 4 and a stiff ring 5 are assembled within the cylinder, the spring 4 being adjacent one of the end caps 2, the ring 5 being adjacent the other end cap and the piston 3 being between the spring and the ring. The piston 3 is made of the same plastic as the cylinder and has a few thousandths clearance between it and the inside walls of the tubular section 1 to provide the time delay restriction. At the center of the piston 3 is an opening 6 of the same or slightly less diameter than the outside diameter of a reduced neck 7 on a piston rod 8. The neck 7 is between shoulders 9 which are spaced apart substantially the thickness of the piston 3. The piston rod 8 has a pointed end 9a which expands the piston as the piston rod is forced through the opening 6. As soon as the piston comes opposite the neck 7, it snaps in place and is positively locked on the piston rod 8. The piston rod extends through tight fitting openings 10 in flanges 11 on reentrant tubular sections 12 on both end caps 2. By making the piston rod of polished or burnished metal such as brass, the tight fit in the opening provides an adequate seal. The pressure between the tight opening 19 and the piston rod 8 increases and improves the seal action during the motion of the piston 3 and piston rod 8, because the reentrant section 12 has a larger area than the seal opening 10.

V In the manufacture of the dashpot, the end caps 2 are heat sealed to the tube 1 after the spring 4, piston 3 and metal ring 5 have been assembled within the tube 1 in the proper relation to each other. At this stage of the assembly, the piston 3 will be held by the spring 4 against the stiff ring 5 which acts as a stop and keeps the piston out of contact with the relatively flexible reentrant section 12 at the right hand end of the dashpot. The cylinder is now filled with a silicone oil of appropriate viscosity and the piston rod 8 is then pushed in from left to right. The pushing thrusts are taken between the piston 3 and the ring 5 so that the remainder of the dashpot is pro tected from strain.

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In the use of the dashpot, when the piston rod 8 is forcibly moved to the left, it is returned by the spring 4 at a rate dependent upon the viscosity of the silicone oil and the clearance between the piston 3 and the bore of the tube 1. With one hundred thousand centistoke silicone oil and a three thousandths clearance between the piston and the bore of the tube, time delays of up to two minutes are readily obtained. These time delays are substantially unatfected by changes in temperature over the range 50 F. to F. There is suflicient flexibility in a radial direction of the axial wall of the reentrant sections 12 so that temperature changes do not build up sufiicient pressure within the dashpot to cause leakage through the openings 10.

The dashpot, except for the spring and plunger, is preferably made from one of the thermoplastic elastomers which permits a closer match to the thermalexpansion of the silicone oil. The flexibility of the tubular reen-' trant sections 12 accommodates any difierence in thermal expansion.

What is claimed as new is:

l. A dashpot comprising a liquid filled cylinder having end caps sealed to opposite ends, a piston having a time delay clearance with the bore of the cylinder, the cylinder end caps and piston being made of a thermoplastic elastomer, reentrant tubular sections on the end caps extending toward each other and having on their inner ends inwardly extending annular sealing flanges, a piston rod fixed to the piston and having opposite ends slidably projecting through the annular flanges, a coil spring surrounding the piston rod and one of the reentrant sections and arranged between the piston and one of the end caps, a stiff annular ring surrounding the other reentrant section and arranged between the piston and the other end cap, said ring projecting beyond the reentrant section it surrounds and transmitting thrust from the piston to the other end cap. I

2. A dashpot comprising a liquid filled cylinder having end caps sealed to opposite ends, a piston having a time delay clearance with the bore of the cylinder and having a center opening, the cylinder end caps and piston being made of a thermoplastic elastomer, reentrant tubular sections on the end caps extending toward each other and having on their inner ends inwardly extending annular sealing flanges, a piston rod of greater diameter than said center opening and having a reduced neck received in said center openings and fastening the piston rod to the piston, said piston rod having thrust receiving shoulders engaging opposite sides of the piston and having opposite ends slidably projecting through the annular flanges, a coil spring surrounding the piston rod and one of the reentrant References Cited in the file of this patent UNITED STATES PATENTS 1,973,706 Hawley Sept. 18, 1934 2,723,846 Holder et a1 Nov. 15, 1955 FOREIGN PATENTS Germany July 28, 1952 I 

